The purpose of a device utilizing this invention is to fill blind holes with viscous products. Filling blind holes with viscous products is difficult due to the fact that air or gas present in the hole, along with the viscosity or surface tension of the product, hinder proper filling of small or narrow holes.
The applications for this device are many: for example it is applicable, but not limited, to fields such as electronics, medicine, connection paths for circuits on circuit boards, . . . It is particularly useful for filling microcavities in space and in military applications.
This patent application is presented in continuation of patent FR00.00008 established on Jan. 3, 2000 submitted by the same applicant, the internal priority of which is claimed.
In order to prevent air that is present in the hole from hindering proper filling by the product, the operation is conducted in a vacuum. The usual method is to place the holes to be filled in a sealed enclosure that is subjected to a vacuum, whereupon the product is forced into the holes using a syringe or dispenser. This technique, although functional, presents a certain number of problems, for example:
the vacuum enclosure must be large enough to contain the injection system, which requires a corresponding increase in vacuum pump size.
It is also necessary to deal with all of the sealing problems between the interior and exterior of the vacuum chamber. This creates a number of difficulties for accessibility and for refilling the device with product, and consequently for the cost of using this type of equipment.
Finally, this type of equipment is not well suited to continuous series production because it requires airlocks for entry and exit between the interior and exterior of the vacuum chamber, or else a step-by-step approach that requires the vacuum to be created again between each step. In any event, this type of equipment becomes extremely complex and expensive.
Moreover, in order to insert a viscous product into a small or narrow hole, the product must be injected under pressure at the openings in order to force filling.
Other techniques have been developed in order to insert products into small diameter tubes or parts that are more or less porous. These techniques described in patents WO9748500A and WO9947260A consist of applying the product to one side of the part to be treated and applying a vacuum to the other side, thereby drawing the product through the part. These techniques are not applicable to filling blind holes and are not transposable to this case.
This invention proposes a solution that is effective and simple to implement. It consists of consecutively and continuously creating a vacuum and then filling right at the hole level, with the filling occurring slightly after the vacuum is created. This is managed essentially by the juxtaposition of two slots in one device. The first slot is connected to a vacuum generator, while the second is connected to a reservoir containing the product. The first slot, which is connected to the vacuum, is simultaneously kept airtight in relation to the exterior and from the second slot by a distance measured parallel to the direction of travel of the device that is larger than the largest opening of the holes to be filled. A perfect seal is made between the surface containing the two slots and the substrate containing the holes to be filled. When the device is moved relative to the substrate, the openings of the holes are sequentially:
isolated in an airtight fashion relative to the exterior of the device,
exposed to the slot connected to the vacuum, creating a vacuum within the holes,
exposed to the slot containing the filling product. Since the product is at atmospheric pressure, it is at a higher pressure when it reaches the opening and is drawn in by the hole until the pressure in the hole is equal to that in the product reservoir. As long as the vacuum is sufficient, the entire hole will be filled with the product.
This device is extremely useful if one wants to fill the holes while avoiding the presence of air bubbles.
Moreover, if the hole openings are not situated in a way that permits the creation of a vacuum between them and the surface of the device, or if one wishes to avoid having the product in contact with the surface of the substrate, a screen can be inserted between the device and the substrate to be filled. The screen can be made of a metallic or synthetic sheet that will be placed in direct and airtight contact with the substrate. It is also possible to use a temporary or permanent screen made from photographic film that is rolled or attached to the substrate.
Likewise it is possible to do silk-screening by inserting a screen between the device and the substrate. In this case, the blind hole is replaced by the gap between the screen and the substrate, and the screen is separated from the substrate after the device has passed, leaving an extra-thick deposit of product on the substrate. This invention can therefore be adapted well to a silk-screen machine and, in such an event, a third slot, identical to the first, can be placed on the opposite side of the second slot so the system can function in two directions, in this case creating the vacuum alternately from the first or third slots depending on the direction of the device""s movement.
Depending on the particular details of the procedure:
Scraping blades can be added before and behind the distribution slot to ensure a better seal for the slot connected to the reservoir. These scraping blades can be made from a single blade that is bent and pierced so that the two ends are located before and behind the distribution slot, while the hole permits the passage of product. A support can be used to strengthen the blades in contact with the surface to be scraped.
To ensure a better seal between the body of the device and the surface to be scraped containing the hole openings, the lower part of the device can be made of a deformable material such as polyurethane, which will conform to surface irregularities and thereby prevent any escape. Naturally, seals placed on the invention device""s active surface can perform the same function.
In order to properly scrape away excess product, a scraping blade can also be set up as a back wall on the device with an angle in relation to the substrate greater than 90xc2x0.
To increase the speed at which the holes are filled by the product, the pressure of the product within the reservoir can be increased.